The invention is related to an in-line valve for a master cylinder, more particularly to an in-line valve which is connected to an outlet of a master cylinder for transferring the oil pressure for braking the wheels, thereby controlling the oil pressure by the resilience of a spring.
In general, a master cylinder generates pressure according to the amount of pressure applied to the brake pedal which brakes the front and rear wheels by the compressed oil. If the same pressure is applied to both front and rear wheels during braking, the rear wheels could jump above the ground. So, to reduce the pressure for the rear wheels an in-line valve is arranged between the master cylinder and rear wheels for controlling the pressure applied the rear wheels.
In FIGS. 5 and 6, as the brake pedal (not shown) is pressed, a push rod 9 pushes a first piston 5 in the left side so as to operate a wheel cylinder (disk) of a rear wheel. A predetermined gap between a first cylinder 5 and a second cylinder 6 is held for preventing the delay of two pistons.
At a portion in which a first piston 5 is placed, a first outlet 11 for discharging compressed oil is provided for braking the rear left wheel, while at a portion in which a second piston 6 is placed, a second outlet 12 for discharging compressed oil is provided for braking the rear right wheel The in-line valve "A", for controlling the pressure of the discharging oil, is installed at the first and second outlets 11, 12, respectively.
The in-line valve "A" is comprised of a body 2 having a first port 2I communicating with the first or second outlet 11, 12 and a second port 2E connecting an oil passage for the rear wheels (not shown). A poppet valve 7 is provided in an opening of the body 2 adjacent to the first port 2I, which is supported by a spring (not shown). A piston 3 is slidably arranged in the body 2 and has a penetrated channel 32 for communicating both the first port 2I and the second port 2E. A resilient means 4 or compression coil spring is provided around the piston 3 and gives force to a support plate 16 fitted in a circular notch 31, thereby pushing the piston 3 toward the second port 2E. In normal mode, an upper end or a ring-shaped end 35 of the piston 3 is positioned away from a protrusion 71 of the piston 7 and so a first chamber 21 formed between the poppet valve 7 and the upper end 35 is communicated with the passage 32. Further, at the second port 2E, a cap 23 is provided for supporting the plate 16 and guiding the movement of the piston 3.
In the above configured in-line valve "A", oil in the master cylinder is compressed as the brake pedal (not shown) is pressed and the compressed oil is transferred to the first chamber 21 through the passage 75 of the poppet valve 7. The compressed oil is further transferred toward the second chamber 22 adjacent to a lower end or a ring-shaped end 37 through the passage 32. Since the area of the upper ring-shaped end 35 is smaller than that of the lower ring-shaped end 37, the piston is pushed up to the first chamber 21 so that the passage 32 adjacent to the upper ring-shaped end 35 is sealably contacted with the protrusion 71. Thus, the transfer of the oil pressure from the first port 2I to the second port 2E is interrupted. That is, the pressure of the master cylinder is transferred to the front wheels at the same value, but is transferred to the rear wheels at a reduced pressure value.
Next, in the interrupted mode, that is, since the second port 2E or the second chamber 22 does not communicate with the first chamber 21, the pressure in the second chamber 22 is held constant. As the brake pedal is continuously pressed, the pressure of the first port 2I steadily increased and the piston 3 is moved to the second chamber 22 so that the first chamber 21 communicates with the second chamber 22. Subsequently, the increased oil pressure is applied on the lower ring-shaped end 37 and the piston 3 is moved up so that the passage 32 adjacent to the upper ring-shaped end 35 contacts on the protrusion 71, thereby interrupting the pressure transfer between the first chamber 21 and the second chamber 22. As a result of the repetition of the above process, the pressure transferred from the master cylinder to the rear wheels is controlled.
As resilient means for supporting the slidable piston in-line valve, a compression coil of relatively long length is employed. In order to reduce the volume of the in-line valve, it is necessary to reduce the length of the spring. To exhibit the same resilient force even in the relatively short length spring the diameter of the wire must be increased. However, if the solid length of the spring having a larger wire diameter is longer than the maximum stroke of the piston, each adjacent wire of the coil spring is excessively contacted in the maximum stroke mode and the coil spring buckles in a traverse direction to the vertical applied force on the end surfaces.